Therefore, for medical wearable
designs, where form factors are crucial
and applications are highly specialized,
the balance of power is tilting toward
more specialized SoC-based solutions.
For a start, the SoC-centric design approach significantly reduces the physical
footprint, a fundamental requirement in
medical wearables.

These SoC solutions minimize power
consumption by separating peak RX/
TX currents from hibernate and sleep
modes that are highly common in
medical products. Battery life is crucial
in wearable healthcare technology, and
these SoCs enhance battery life with
very low-current sleep modes.

Moreover, these chips come with a
fine-tuned RF performance, which saves
the development time and allows developers to make changes at the software
level without modifying hardware. And
that helps improve radio sensitivity,
expand the range, and reduce overall
layout size. Nordic’s nRF52840 chip,

The good news for wearable designers
is that single-chip solutions are now available that integrate Bluetooth 51 (
Blue-tooth® low energy), ANT™ and 2. 4 GHz
proprietary wireless technology. One
such example is Nordic Semiconductor’s
nRF52840 chip that combines a 32-bit
ARM® Cortex® M4F processor with a
2. 4 GHz multiprotocol radio. It provides
ultra-low-power wireless connectivity and
compute cycles for the in-ear thermometer shown in Figure 1.

Bluetooth low energy is a clear winner
when the amount of transferable data is
small, and the wearable device is paired
with a host: a smartphone, tablet or
medical hub. But what about standalone
wearable devices and the ones transporting larger chunks of data? The actual data
throughput of BLE links is usually far less
than the 1 Mbps and 2Mbps theoretical
speeds. The practical data transfer rate
of a Bluetooth 5 link, depending on the
application, has been recorded around
300 Kbps.

Enter Wi-Fi Connectivity.

Here, like BLE, there are chipsets
available that integrate multiple Wi-Fi radios with an application processor. These
system-on-chip (SoC) solutions integrate
a low-power host processor (typically an
ARM Cortex core) and an IEEE 802.11n
MAC/baseband/radio. Depending on the
level of integration, the solution may also
include a transmit power amplifier (PA)
and a receive low-noise amplifier (LNA).

These chipsets—such as CYW43907
from Cypress Semiconductor—support all
Wi-Fi rates specified in the IEEE 802.11
a/b/g/n specifications. And they make
use of advanced techniques to reduce
active and idle energy consumption in
order to bring the power bar low enough
to serve wearable medical designs.

Module or System-On-Chip?

One of the fundamental questions that
wearable designers face is whether to use
an SoC approach or purchase a third-par-ty module. A pre-packaged module is a
solid option for incorporating wireless
connectivity because of inherently difficult RF and antenna design.

The wireless modules (Figure 2) are
tested, calibrated and pre-certified, and
thus remove a tremendous amount of design complexity while bypassing the need
to specify components such as filters,
amplifiers, clocks, capacitors, inductors,
crystal oscillators, and antennas.

Specifically, for wearable designs,
the conventional wisdom dictates that
small-volume developers should opt
for such plug-and-play modules. Apart
from being economical, wireless modules can also cater to design challenges
related to system layout, software stack
development, device security, connection
reliability, and signal interference and
degradation.

In other words, wireless modules,
apart from providing certifications under
various regulations in different countries,
can also act as an RF consultant for your
wearable design. Especially, when it
comes to tricky analog front-end issues
such as antenna design and network
matching circuitry.

However, the Bluetooth antenna, which
is integrated into the module, has to be
implemented in a specific position with a
specific output profile. If the BLE antenna
gets buried in a wrong place on the board,
it could seriously impact radio performance and subsequently the battery life.